Internal combustion engines designed to achieve a useful power output through the control combustion of solid powdered fuels, such as coal, have been proposed and fabricated in prototype stages essentially since the early investigations of Rudolph Diesel. Generally, the difficulties encountered by investigators in connection with these engines have centered about the development of techniques for forming and controlling a particulate fuel-air mixture for introduction in properly timed fashion into a combustion chamber.
In typical engine design approaches, a particulate formed of powdered coal and air is conveyed to an intake manifold, pre-combustion chamber or the like, whereupon the suspension is directed to a combustion region for ignition. The maintenance of the particulate suspension during this procedure has been seen to be difficult, resulting in unwanted powder accumulation and degradation of desired fuel-air ratios. Approaches intended to maintain a proper particulate suspension have included, for example, "animators" serving to agitate particles within the suspension as it awaits introduction to the region of combustion. Loss of consistency in a predetermined and desired suspension necessarily results in a loss of accurate metering of fuel into the combustion chamber leading to vagaries in cylinder power output.
Another operational difficulty typically encountered in the past stems from the utilization of conventional valve structures. Such structures may not close tightly, inasmuch as dust particles tend to build up upon the seating surfaces thereof. Accordingly, the submission of the particulate fuel suspension to the combustion chamber of the engines preferably should be under the control of valving which is immune from deficient operation resulting from clogging or particle buildup.
Because solid particulate fuel such as coal dust is available in bulk form and is subject to varying degrees of bulk compaction and moisture content, it is necessary that engine support systems utilizing the coal powder be capable of transporting it in predictable and uniform fashion. Where dynamic variables are involved in this transportation, opportunity exists for the loss of desired air-fuel ratios and consequently undersirable engine performance. Related hindrances to the desired operation of the engines develop in the course of carrying out throttling functions. Where throttling procedures are performed upon the particulate fuel alone, i.e., not in suspension, somewhat downstream of combustion, lags and inaccuracies may result in consequence of the nature of the fuel delivery system itself as well as in variations in the consistency of the bulk fuel. On the other hand, where throttling occurs as a control over the amount of particulate suspension submitted to the combustion chamber, then valving difficulties may well be encountered.
Concerning the handling and storage of fuel itself, coal dust obtained from the mine production environment may exhibit varying degrees of moisture content. Even where this mositure content can be standardized, the storage of the dust may lead to variations of that value in view of the wide geographical regions within which it may be used. Such variations in moisture content pose vagaries which must be accounted for in connection with the delivery system of the fuel at the side of the engine. Thus, the characteristic of the fuel itself is not entirely uniform, a condition requiring a different form of fuel handling than industry has been acquainted with heretofore in conjunction with reasonably uniform liquid base fuels. However, in view of the growing costs associated with fluid hydrocarbon fuels, and in view of the very low cost of coal dust as a fuel, a practical internal combustion engine powered by coal dust now represents a viable alternative source of power.